Aqueous calcium stearate dispersions have long been used as additives in paper coating formulation, the calcium stearate imparting lubricating, leveling and anti-dusting properties to the coating formulation.
Since it is preferable in the paper making industry to use as many predispersed starting materials as possible in preparing various coating formulations, it is advantageous to provide aqueous calcium stearate dispersions having as high a solids content as possible. Such advantages inure in lower shipping costs and introducing less water into the coating formulation.
It is reported that conventional aqueous calcium stearate dispersions containing much above 50 to 55 weight percent solids do not retain desirable rheological properties, i.e., they are quite viscous and difficult to handle and meter. Efforts have therefore been directed to preparing aqueous calcium stearate dispersions having a high solids content, i.e., higher than 55 weight percent.
Some such high solids content calcium stearate compositions having workable viscosities are reported in U.S. Pat. No. 4,659,489 and 4,676,836. U.S. Pat. No. 4,659,489 discloses high solids content, i.e., 50 to 75 weight percent, aqueous dispersions containing calcium stearate, dispersing agent, non-ionic lubricant and urea. U.S. Pat. No. 4,676,836 describes similar compositions, except that anionic lubricant is used in place of the non-ionic lubricant of U.S. Pat. No. 4,659,489. Copending, commonly owned U.S. application Serial No. 07/448,787, filed Dec. 11, 1989 also discloses high solids content, i.e. 60 to 80 weight percent, aqueous calcium stearate dispersions containing calcium stearate, urea and starch syrup.
A possible disadvantage to such urea containing high solids calcium stearate dispersions is that urea, in aqueous solution, slowly hydrolyzes to ammonium carbamate. Moreover, prolonged heating of aqueous urea solution results in formation of biuret and liberation of ammonia. Also, urea containing high solids calcium stearate dispersions tend to colorize, i.e., turn from white to yellow, on prolonged standing. Consequently, it is desirable to provide, as does the present invention, urea-free, high solids content, aqueous calcium stearate dispersion.